Many parents observe their newborn babies have light-colored eyes, often appearing blue or bluish-grey. This common observation has led to a widespread belief that all infants are born with blue eyes. However, the reality of infant eye color is more nuanced, involving complex biological processes that determine the final hue.
The Truth About Newborn Eye Color
The notion that all babies are born with blue eyes is a common misconception. While many newborns, particularly those of Caucasian descent, may exhibit blue or bluish-grey eyes at birth, this is not universally true. A 2016 study, for example, found that nearly two-thirds of newborns were born with brown eyes, while only about 21% had blue eyes. This initial light appearance is often due to a temporary lack of melanin, the pigment responsible for eye color, in the iris.
The blue or grey appearance results from light scattering rather than the presence of blue pigment. When there is little melanin in the front layers of the iris, light entering the eye is scattered, and shorter blue wavelengths are reflected back, making the eyes appear blue. As melanocytes, the cells that produce melanin, have not yet fully activated, the amount of pigment in the iris is initially low. Babies with darker skin tones are frequently born with brown eyes, indicating a higher melanin presence from birth.
The Science Behind Eye Color
Eye color is primarily determined by the amount and type of melanin present in the iris. There are two main types of melanin: eumelanin, which produces brown and black pigments, and pheomelanin, which produces red and yellow pigments. The concentration and distribution of these pigments within the iris’s stroma dictate the eye’s color. A high concentration of eumelanin leads to brown eyes, the most common eye color globally.
Eyes with less eumelanin may appear green or hazel, often involving pheomelanin. Blue eyes contain very little melanin in the front layers of the iris. The blue appearance is a structural color resulting from Rayleigh scattering, similar to how the sky appears blue. Light enters the iris, and in the absence of significant pigment to absorb it, the shorter blue wavelengths are scattered and reflected more than other colors, making the eyes look blue. The genetic makeup inherited from parents influences melanin production, determining an individual’s eye color.
When Eye Color Becomes Permanent
A baby’s eye color is not fixed at birth and can change significantly over the first few months, or even up to a year or more. This dynamic change occurs as the melanocytes in the iris respond to light exposure and begin to produce more melanin. Since infants spend time in the dark womb before birth, their melanocytes have not been fully stimulated, resulting in lower melanin production initially. As eyes are exposed to light, these cells gradually become more active.
The most noticeable changes in eye color occur between 3 and 9 months of age, with many babies’ permanent eye color established by their first birthday. Subtle shifts can continue until a child is around three years old, and in rare cases, even into adulthood. Eye color changes usually progress from lighter to darker; for instance, blue eyes may turn green, hazel, or brown, but brown eyes will not lighten to blue. The ultimate eye color is largely determined by the genetic instructions for melanin production that the baby inherits.